The invention relates to an apparatus and method for retarding internal combustion engines, typically diesel engines, by releasing compressed gases from each cylinder through an exhaust valve near the top dead centre position of a compression stroke and at the same time, opening the exhaust valve of a cylinder on an intake stroke.
Truckers commonly encounter the problem of slowing heavy trucks, usually diesel-powered trucks, on long downgrades. It is well known that excessive use of conventional brakes leads to premature brake wear and to overheating of the brakes. Consequently, it is well known to slow trucks with diesel engines by compression release retarding devices. These devices operate by cracking open each exhaust valve just prior to top dead centre of each compression stroke with the fuel supply to the engine cut off. The compressed gases are then diverted into the exhaust manifold, instead of being retained in each cylinder, which would provide an undesirable rebound effect and cancel the braking effect of the compression stroke.
Patents have been issued for engine braking devices of this type, including the following U.S. patents assigned to Jacobs Manufacturing Company:
______________________________________ 4,592,319; 4,339,787; 4,398,510; 4,473,047; 4,423,712; 4,395,884; 4,474,006; 4,485,780; 4,510,900 and 4,572,114. ______________________________________
There is also U.S. Pat. No. 4,655,178 issued to the present inventor.
My own previous U.S. Pat. No. 4,741,307, issued May 3, 1988 discloses the principle of opening an exhaust valve of a cylinder on the intake stroke while cracking open an exhaust valve near top dead centre of a compression stroke. This causes the gases from the cylinder on the compression stroke to be diverted into the cylinder on the intake stroke, thus increasing the charge received in each cylinder. When that same cylinder reaches the compression stroke, there is more charge in the cylinder, thereby increasing the braking effect as the gases are compressed. In this previous patent, hydraulic means was employed to operatively engage all of the exhaust valves of a group of cylinders, such that all of the exhaust valves of that group of cylinders are opened simultaneously. The exhaust valve of a first cylinder is cracked open when the cylinder is near top dead centre of a compression stroke, the other two cylinders being on the intake stroke and exhaust stroke respectively.
It is known to retard engines using an exhaust restrictor. Exhaust restriction in itself provides a braking effect by providing a back pressure when each cylinder is on the exhaust stroke. In any previous application, Ser. No. 07/189,292 an exhaust restrictor was used to raise pressure in the exhaust manifold sufficiently to pop open exhaust valves of cylinders on the intake stroke.
It is also known to provide an adjustable nozzle or diverter on the turbine of a turbocharged internal combustion engine equipped with a compression relief brake. The adjustable nozzle or diverter restricts the flow of exhaust gases to a limited portion of the turbine only. The purpose in doing this is typically to increase the velocity of gases entering the turbine to increase the turbine speed and thus the compressor speed when the engine being braked. This increases the volume of air drawn into the engine and therefore the compression load and braking effect. A diverter of this type is shown, for example, in Federal German patent application No. 28 20 940 Published Nov. 23, 1978. The U.S. Pat. No. 4,474,006 to Price issued Oct. 2, 1984 discloses the use of a diverter valve to divert the exhaust gases to one portion of the divided volute of the turbine. U.S. Pat. No. 4,395,884 to Price issued Aug. 2, 1983 discloses the use of a diverter valve to divert all of the flow of the exhaust gases into one portion of a double entry turbine. These previous patents do not disclose an adjustable nozzle or diverter which provides sufficient pressure in the exhaust manifold to achieve the opening of exhaust valves for cylinders on the intake stroke and thus derive benefits similar to those of my earlier invention in U.S. Pat. No. 4,741,307.